A step of supplying a process gas in a predetermined decompressed atmosphere is often employed in processing a substrate such as a semiconductor wafer This process is often performed by disposing the substrate in a processing chamber capable of maintaining a decompressed atmosphere. In general, many steps are included in processing a substrate. Plural processing chambers for performing the steps are connected to a substrate conveying chamber, in which a substrate is conveyed into a processing with a conveying mechanism such as a robot provided in the conveying chamber, and is conveyed out from the processing chamber to another processing chamber.
This substrate processing apparatus is generally referred to as a cluster tool. In general, plural processing chambers and load-lock chambers are disposed at a periphery of a conveying chamber, and a robot in the conveying chamber performs conveyance of a substrate via an arm. The load-lock chamber is a pressure-adjusting chamber for conveying a substrate into a conveying chamber from the outside, and conveying a substrate out from the conveying chamber to the outside. That is, since the conveying chamber is connected to the processing chamber, the inside of the conveying chamber is required to maintain a decompressed atmosphere similar to the atmosphere in the processing chamber. Therefore, the load-lock chamber is provided to isolate the ambience in the conveying chamber from the outside.
With the above-described cluster tool, there is a limit in the number of processing chambers which can be arranged, since the processing chambers and the load-lock chamber are required to be arranged in a manner surrounding the conveying chamber. For example, in a case of a conveying chamber having a pentagon shape when viewed from above, the number of chambers that can be connected to the conveying chamber is limited to one load-lock chamber and four processing chambers, where each processing chamber is connected to one side of the pentagon. Although the number of sides connectable to a processing chamber can be increased by employing a polygon having same or more sides than a pentagon as the shape of the conveying chamber, one of the sides becomes smaller than the size of the processing chamber. As a result, the processing chamber cannot be connected. Accordingly, the number of processing chambers that can be arranged is limited for a conventional cluster tool, and thus, there is a problem of being unable to handle processes such as a process of consecutively performing numerous steps or a process of simultaneously performing a single or numerous steps in parallel.
In order to solve this problem, an increase in the number of processing chambers by connecting two cluster tools, for example, is proposed. However, even with this configuration, the number of connectable processing chambers is limited. In addition, a mechanism for conveying a substrate from one cluster tool to another is required, which thereby complicates and enlarges the configuration of the apparatus.
Furthermore, since the space of the conveying chamber becomes larger as the number of processing chambers increases, a pump having large throughput is required for maintaining a decompressed atmosphere in such a large space, thereby raising a problem of increasing cost.